Biodistribution and dosimetry of carbon-11-methoxyprogabidic acid, a possible ligand for GABA-receptors in the brain.
Carbon-11-methoxyprogabidic acid (11C-MPGA) was recently synthetized as a possible ligand for PET studies of gamma-amino-butyric acid (GABA) receptors in the brain. The data for human absorbed dose estimates are calculated based on the biodistribution of 11C-MPGA in mice and humans.


METHODS
Eighteen mice were killed at preset time intervals after an intravenous bolus injection of 3.7 MBq (100 microCi) 11C-MPGA. Time-activity curves were reconstructed for several organs. Three healthy men each had whole-body PET scans after an intravenous bolus injection of 37 MBq (1 mCi) to determine activity in the critical organs. Animal data were fitted into these human findings to calculate residence times, and the MIRDOSE 3 protocol was used to calculate the radiation absorbed dose.


RESULTS
Animal studies demonstrated a rapid distribution of 11C-MPGA in several organs. The highest activity was detected in the intestines, liver and kidneys. Brain activity was low throughout compared to these organs. The human whole-body study yielded similar results, with the intestines, liver and kidneys showing the highest activity. The estimated dose to the urinary bladder compartment turned out to be significant. The mean effective dose was 4.8 microSv/MBq (s.d.= 0.5 microSv/MBq).


CONCLUSIONS
PET studies using 185 MBq (5 mCi) 11C-MPGA are within the International Commission on Radiological Protection risk Category II for healthy volunteers.
Santens
P
P
PET Center, University Hospital and University of Gent, Belgium.
De Vos
F
F
Thierens
H
H
Decoo
D
D
Slegers
G
G
Dierckx
R A
RA
De Reuck
J
J
D000328:Adult; D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism*; D002250:Carbon Radioisotopes; D006801:Humans; D008297:Male; D051379:Mice; D018079:Receptors, GABA / Q000032:analysis*; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed; D005680:gamma-Aminobutyric Acid / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
D002250:Carbon Radioisotopes; D018079:Receptors, GABA; D005680:gamma-Aminobutyric Acid